An HEV is a vehicle that has a propulsion system that consists of at least one electric motor or electric machine in combination with at least one other power source. Typically, the other power source is a gasoline or diesel engine. There are various types of HEVs depending on how the electric motor(s) and other power source(s) are combined with one another in order to provide propulsion for the vehicle, including series, parallel and compound HEVs, including those having electrically variable transmissions (EVTs) which provide for continuously variable speed ratios by combining features from both series and parallel HEV powertrain architectures.
The development of new HEV powertrain architectures also facilitate the development and implementation of novel vehicle operating methodologies that utilize the novel features available in these systems. New operating methods are desired that utilize HEV powertrain architectures, for example, to provide vehicle operating methodologies that are particularly adapted to their operating environments, or that meet legal, regulatory or other constraints that are imposed upon their operating enviroments, such as by using novel combinations of electrical and mechanical propulsion energy to minimze vehicle emisssions, such as noise and exhaust emissions. It is also desirable that such operating methodologies are incorporated into the vehicle hardware and software systems as novel operating modes that are available for selection manually by an operator, or for automatic implementation by the vehicle in response to predetermined conditions.
Complex EVT HEVs utilize one or more electric machines and require advanced, high energy density, energy storage systems (ESS) which include batteries, ultracapacitors or combinations thereof, to supply electrical energy to and receive and store electrical energy from these machines. The implementation of new operating methodologies, place increased demands on the electric machines and ESS associated with the dynamic flow of power into and out of the ESS.
Therefore, it is highly desirable to develop vehicle operating methodologies that are adapted to vehicle operating environment requirements and that can be incorporated into the vehicles as operating modes that implement advance control of HEV systems, including the engine, electric machine and ESS systems. It is particularly desirable to implement a silent or hush mode whereby the electric machine is used preferentially to power the vehicle and the engine output power is generally limited to a value that is less than the maximum engine output power.